Not sure when you say "intended" if you mean that it is textually or necessarly intended that one singer be an African American woman and one be a Caucasian woman, or if you mean that it was originally cast that way?
But you may want to look at:
The duets for Rose and Caroline in CAROLINE OR CHANGE
Gettin' a Man from SARATOGA
any duets (?) for Catherine and Dollie or any other white woman in THE GRASS HARP
Can't Hell Lovin' Dat Man Of Mine (not exactly a duet) from SHOW BOAT
any duets (?) for Jewel and Mona in THE BEST LITTLE WHOREHOUSE
if you consider Amneris as a role intended for a white actress, then, as already suggested, My Strongest Suit from AIDA
if you consider Kate as a role intended for a black actress, Best Friend from THE WILD PARTY
Here Within These Walls from SISTER ACT
Go Home from THE LIFE
There might be some in the musical of GONE WITH THE WIND
His Eye is On The Sparrow - classic song sung by Frankie and Berenice (with John Henry) in the play THE MEMBER OF THE WEDDING, and it's a safe bet that, if you can fine them, there are duets for Frankie and Berenice in Mary Rodgers's musical adaptation, F. JASMINE ADAMS
Updated On: 8/24/16 at 11:50 AM